The present invention relates to optical cards in which information recorded on the optical cards is optically read and, more particularly, to a card technique which makes difficult identification, in external appearance of an optical card from other cards such as magnetic cards. IC (integrated circuit) cards and the like.
In recent years, utilization of cards increases abruptly. In response to the increase in the cards, types or kinds of the cards also increase. The main current is a magnetic stripe card, that is, a magnetic card, with exception of the above, attention is made to an IC card having a larger storage capacity and a higher security function and an optical-data recording card, that is, an optical card having a storage capacity which is larger a few hundred times than the IC card.
These various cards are common to each other in that a data recording section is provided on a card substrate which has its rigidity as the card. Each of the magnetic stripes of the magnetic card and the memory in the IC of the IC card forms the data recording section. Further, in the optical card, the optical-data recording pattern, which is made of material high in light reflectivity, forms an optical-data recording section. Accordingly, from a difference of the optical data recording section or other sections, it is easy to identity the type or kind of the cards by observation of the external appearance of the cards. Particularly, in the optical cards, that is, in the read-only optical card there among, a portion of the optical card has light reflectivity which is extremely high. For this reason, it can easily be understood that a glance at the card shows an optical card.
By the way, in order to prevent the card from being formed or being abused, it is desired that cards different in type from each other are difficult to be identified on external appearance. This also has a sense from the viewpoint of increasing a commodity value.
From the points of view referred to above, in the conventional optical card, identification of the card can easily be grasped by observation of the external appearance of the card, since the optical-data recording section can be viewed from the reading side, The optical-data recording section cannot originally be viewed from a side of the optical card, which is opposite to a side thereof upon which the reading light is incident.
As a technique which makes the types of the cards difficult to understand, a way is considered in which the recording section is concealed. Regarding a magnetic card, U.S. Pat. No. 4,182,350 discloses a technique in which a color layer is provided just on a magnetic stripe that is a recording section, to conceal the color peculiar to the magnetic stripe, thereby increasing a sense of beauty.
If, however, an optical-data recording section of an optical card is concealed simply by the color layer disclosed in the above-mentioned U.S. Pat. No. 4,132,350, that is, by a shielding layer, the shielding layer will interfere with reading of the optical-data recording section. Particularly, if the shielding layer is provided adjacent the optical-data recording section, a delicate change will be given to a viewer in the viewpoint of external appearance by reception of an influence of variation in the shielding layer or an influence of a light-reflective pattern of the optical data recording section. That is, a delicate change is given to light reflected from the optical card. By the change, the viewer knows what is present below the shielding layer. This is considered as follows, That is, in case of the magnetic stripes, the entire stripes are formed by a layer which is substantially even or uniform in thickness, while the optical-data recording section of the optical card has irregularity because the light-reflective pattern indicating the information is formed in the optical-data recording section of the optical card. That is, in the optical card, at any cost, delicate irregularity will remain on the surface of the layer of the optical card, or interference of the light will occur by influence of the light-reflective pattern. In case of the optical card, accordingly, the shielding layer cannot but be formed thick considerably so as to eliminate the irregularity. If the shielding layer is thick, however, the uniformity in thickness of the entire shielding layer tends to be damaged and, accordingly, there is a fear that a problem occurs in reading of the optical card.
As the optical card. Japanese Pat. Provisional Publication (Kokai) No. SHO 02-298036 discloses such a technique that a light-colored coloring layer is provided adjacent the optical-data recording section, that is, just on the latter, thereby increasing advantages of design. However, this technique can be said to a technique in which a metallic color of the optical-data recording section can be viewed through the coloring layer. Thus, a viewer can easily identify that the card is an optical card.